Pitfalls and benefits in NZ First-Labour coalition Government

New Zealand First has backed the Labour Party into power, led by last-minute leader Jacinda Ardern, who has steered the party to an incredible victory.

Labour and NZ First will form a full coalition Government, with the Greens' support on confidence and supply.

With Labour and NZ First working together in coalition, NZ First has secured four powerful ministerial roles inside cabinet. It's not yet been announce what those roles are, but Mr Peters said all NZ First ministers would be inside cabinet.

Mr Peters himself has been offered the role of Deputy Prime Minister, which he is considering.

NZ First could have entered into either a coalition agreement or a confidence and supply arrangement with Labour.

A coalition deal sees NZ First linked more closely to Government decisions, which can be risky, especially if policy is unpopular with voters.

The upside to a coalition deal for NZ First would be policies and positions - they will get backing from the Government on major policies.

Under the coalition, Mr Peters is expected to make significant policy gains.

That's likely to be policy around immigration and housing, two major policy platforms for NZ First. Both Labour and NZ First want to build more houses and reduce immigration - although NZ First wants to cut immigration levels much more drastically.

Mr Peters said the Green Party would support the coalition Government under confidence and supply.

For the Greens, that means they will have to support the Government's budget - that's the supply half - and on confidence, if a vote of confidence in the Government was to be raised.

The Greens will be at arm's length of the Government, meaning they could vote against policy - aside from the Budget - if they choose to.

Mr Peters said the Greens are not in the coalition agreement, because "it is a Labour-NZ First Government."

This could be beneficial for the Greens - this election saw votes leak between the Greens and Labour. The Greens could make a point of difference by voting against Labour on policy that's unpopular with Green or Green-sympathetic voters.

The Greens will get Ministerial portfolios under the agreement, Ms Ardern said.

The National Party will form a huge opposition in Parliament, as the single party that took the most votes.